- [Instructor] Azure Load Balancers createa highly available structure by distributing trafficamong healthy virtual machines within the network.In Azure, we have two load balancers.We have an Internet Load Balancerand an Internal Load Balancer.In our example here, I'm showing you both load balancers.As we work from the top down, traffic would enterour first load balancer,which is our Internet Load Balancer.This would have a public IP address associated with it.The traffic would then be distributedacross the virtual machines within an availability set.

Traffic that then needed to be directed to ourlower database tier would pass throughan Internal Load Balancerand the same process would be repeated.The traffic would be distributed equallyamong the virtual machines within that tier.These virtual machines are in an availability set.One thing you will notice here, though,with our Internal Load Balancer,we have another connection.This would be for our external users,let's say our on-premise environment.These users would connect directlyinto the Internal Load Balancerand then their traffic would be distributedacross those virtual machines,instead of them going out through their gatewayand then coming back in through ourInternet Load Balancer.

The load balancers will only distribute trafficto healthy virtual machines,or instances, within the balance set.We use Probes to do this,and they just monitor those virtual machines.If a machine is deemed unhealthy,new requests will not be sent to it,and the traffic will continue to be directedto the healthy virtual machines.Machines are deemed unhealthyif HTTP 200 OK is not returnedwithin the specified timeout.The endpoints of virtual machines are probedevery 15 seconds and the default timeout is 31 seconds.

If the load balancer does not receive the responsewithin that timeout, it will be deemed unhealthy.And we have two types of probes.We have an HTTP Probe and a TCP Probe.When you use an HTTP Probe, the instance, or virtual machinewill be deemed unhealthy if the application respondswith a code that is not 200,or if a response hasn't been receivedwithin the specified timeoutor if TCP is reset.A TCP Probe uses a three-way handshaketo initiate communication.And just like the HTTP Probe,if the server does not respondin the specified timeout period,or TCP is reset,the virtual machine or instance will be deemed unhealthy.

Within our load balancers,we also have load balancing rules.Basically, this directs traffic based on a port.We can also enable session persistencewithin the load balancing rules.This guarantees that the client will always connectto the same virtual machine instance during the session.We can also enable floating IP,or sometimes you'll hear it referred to asDirect Server Return.This would be enabled when configuringa SQL Always On availability group listener.Otherwise, leave the default of disabled.And finally, we can configure NATwithin our load balancers.

NAT will allow us to direct specific trafficto a specific VM.For example, you have clients on the internetwho need to RDP into that virtual machine,you could set the rule up in the load balancerthat when that traffic on that portenters the load balancer,it is then directed to the corresponding port on the VM.And that's the overview for load balancers within Azure.

Resume Transcript Auto-Scroll

Author

Released

3/16/2017

Become skilled in configuring virtual networks, modifying network connections, and implementing multisite or hybrid networks using Microsoft Azure. See how to design and implement virtual networks, configure solutions on-premises, administer VMs, manage load balancing, and more. Learn how to set up gateway VPNs, VNet, and site-to-site connections. The course is also an exam preparation resource for the 70-533 exam: Implementing MS Azure Infrastructure Solutions.